1. Field of the Invention
The present invention generally relates to a detector module for measuring the angular position of an incoming signal and, in particular, to a position sensing module using fiber optic tapers and single element detectors.
2. State of the Art
Many systems designed to measure and/or track the angular position of an optical signal, for example a laser spot, make use of a quadrant cell detector. Quadrant cell detectors are generally known in the art and are normally monolithic chip structures with the sensitive elements created by doping selected areas of the chip and by leaving an area on the order of 100 xcexcm wide undoped between the selected areas. Obtaining sufficient isolation between the channels in quadrant cell detectors for high sensitivity seekers and spot trackers often leads to very complex and expensive electronics designs. Moreover, currently available silicon quadrant cell detectors are relatively small, on the order of 1.5 mm in diameter, which presents a small active detecting area thereby limiting their usefulness for angular position sensing and spot tracking applications.
Another conventional way of determining the location of an incoming signal is through the use of detector arrays. Typical detector arrays include quadrant arrays and large area detectors that provide differential output, commonly known as Position Sensitive Detectors (PSD).
PSD""s are normally monolithic PIN photodiodes with either one or two applied uniform resistive surfaces. When a light spot falls on the PSD, an electric charge is generated at the incident position and read out through the resistive surfaces. The photocurrent read out is inversely proportional to the distance between the incident position and the electrode, thus providing a means to measure the incident position. The effectiveness of conventional arrays of PIN photodiodes is limited due to the relative lack of sensitivity and long response time of the PIN sensors.
Thus, the usefulness of the above-described conventional detectors especially for optical angular position sensing applications, is often limited by the physical characteristics of the detectors, such as physical size, sensitivity, response time, and electrical and optical cross-talk and noise.
Accordingly, it is desirable to provide a position sensing module that overcomes the above-recited drawbacks and difficulties associated with conventional detectors.
It is an object of the present invention to use individual detectors that provide a high degree of both optical and electrical isolation between the detectors instead of a quadrant array or a large position sensitive detector, without requiring very complex and expensive electronics designs.
It is also an object of the present invention to easily and cost effectively integrate a high speed laser rangefinder detector and a high sensitivity laser spot tracker into a single module.
In accordance with the principles of the present invention, the position sensing module of the present invention overcomes the above-described limitations of conventional detectors, and others, by providing detector modules having lower cross-talk noise and higher sensitivity, while allowing for the incorporation of commercially available components and techniques.
According to the present invention, an incoming optical signal is transferred to one or more independent, electrically isolated detectors to provide the angular position measurement capability of a standard quadrant detector array or a position sensitive detector. The optical signal is received and transferred by fiber optic tapers. Fiber optic tapers are manufactured by precisely heating and stretching a fused bundle (or boule) of optical fibers. The resulting xe2x80x9chourglass-shapedxe2x80x9d component is then cut and polished to provide the desired small/large surface area ratio. Fiber optic tapers will either magnify or minify an image, depending on the direction of propagation through the taper, with the amount of magnification determined by the ratio of surface areas.
The present invention includes a position sensing module comprising:
a plurality of fiber optic tapers, each having a first surface, a tapered section and a second surface, said first surface having a larger surface area than said second surface;
a plurality of position sensing detectors, each detector mounted to the second surface of a respective fiber optic taper.
The invention also includes a module for high speed laser rangefinding detection and high sensitivity laser spot tracking comprising:
a plurality of fiber optic tapers, each having a first surface, a tapered section and a second surface, said first surface having a larger surface area than said second surface;
a plurality of position sensing detectors, each detector mounted to the second surface of a respective fiber optic taper; and
a rangefinding detector coupled to an optical fiber.